The present invention relates to improvements in electroless plating of polyamides. In our pending U.S. application Ser. No. 06/159,585, incorporated herein by reference, there is disclosed and claimed a process for preparing the surface of polyamide substrates for electroless plating, comprising forming a conditioned polyamide substrate by etching with an aqueous alkaline conditioning solution having a pH of at least about 10 and maintained at 150.degree. F. to the lesser of the boiling point of the solution and the softening point of the polyamide substrate for a time sufficient to render the substrate receptive to etch by an organic acid. This is followed by etching of the conditioned polyamide substrate with an aqueous acid etch solution preferably comprising at least one organic acid containing from 2 to about 10 carbon atoms in the molecule and present in the aqueous solution in a concentration of at least about 3 percent by weight of solution. The process renders the conditioned polyamide substrate uniformly and directly receptive to a metal electroless plating catalyst and is adaptive to the treatment of Nylon 6 and Nylon 6,6. Where the substrate is a caprolactam polymer, etching can be achieved without contact with the aqueous alkaline conditioning solution and, as described in Application Ser. No. 06/159,503, is preferably accomplished with the use of the aqueous solution of an organic acid containing from 2 to 4 carbon atoms in the molecule. Trichloroacetic acid is the presently preferred organic acid. Adhesion to a substrate is enhanced by increased concentration of the acid etchant or prolonged contact time. Because some organic acids are solvents for the polyamides, there is a tendency in their use for the substrate surface to absorb the organic acid. This can induce surface softening and, if extensive, will form, for a period of time, a soft, easily scored surface.
A need has existed to improve adhesion to the surface of the polyamide substrates treated in accordance with the process of the above-identified applications, while avoiding surface softening.